Promise ring

Hello guys i have been in a relationship for a year now i (26m ) and she is (28 f) unfortunately i cant marry her because of my financial situation and she told me she wants a promise ring as a joke but i think she wasnt 💀 so im thinking to get her one, do you guys know any good places that sells them? Her birthday is in a couple of months should i gift that to her ? Or give it in our next date and get her something else for her birthday?